Talk:Apparent wind

Rewrite

I have rewritten to remove ambiguity and to clarify the physics of the situation

Tayana 20:44, 19 September 2006 (UTC)

Hi Tayana! I have a small nit to pick. You added the text "must be trimmed to so that they", and now the resulting text says "it determines the points of sail on which the sails must be trimmed to so that can they can efficiently generate forward motion".

This particular edit is confusing, because it implies that points of sail are the same as sheeting angles. At least in my experience, the point of sail refers to a potential course the boat can take, not the trim of the sails. (Though the former determines the latter, obviously.)

I think this edit is also a bit misleading, because it implies that sails can be trimmed to be effective on any point of sail. In fact, apparent wind doesn't merely determine sail trim, it also determines the directions a boat is able (and unable) to go. See Points of sail, particularly where the diagram shows the "No go zone". Apparent wind is one of the factors which determines the angles of the lines on that chart, and if you try to point the bow of the boat on a course inside the red pie-wedge, you won't go anywhere. (At least, not efficiently.) That's what I originally was trying to say in that paragraph.

Infinoid 15:16, 20 September 2006 (UTC)

Maybe the question would be more easily settled if we knew from which source the information is being drawn off. -- Rune Welsh | ταλκ 19:59, 20 September 2006 (UTC)

Hi, Rune.welsh! I'm not sure exactly what "question" there is... I just think Tayana's clarification removes some useful information from the article, specifically, that apparent wind will change the angles of the "No go zone" (again, see Points of sail). Having more velocity (and therefore, more apparent wind) will make the "No go zone" larger, meaning you have to steer the boat a little farther away from directly upwind in order to keep moving. Apparent wind isn't the only factor determining the angles a boat will begin to luff at, but it is an important one. Therefore apparent wind doesn't only affect the sails, but also the course of the boat itself, which I feel is no longer conveyed accurately by the article text.

I don't know how to provide a source for this information, as I was taught sailing (and sailboat racing) through hands-on practice and talking with other crew members. I suppose its possible to prove it mathematically, and I can do this if it would help. Please clarify, I don't know what information I should provide. Should I just add further clarification to the article? I don't want to undo Tayana's (very useful) work... Thanks! Infinoid 22:33, 20 September 2006 (UTC)

• • The article is about Apparent Wind only. Information about points of sailing and sheeting angles for different courses is more appropriate in categories Points of sail or Sailing

Tayana 23:02, 20 September 2006 (UTC)

• • • Wikipedia is not paper and thus we are not limited to space constrains. If the mention of points of sail in relation to apparent wind is relevant to the article (as Infinoid suggests) then it probably deserves to be mentioned. -- Rune Welsh | ταλκ 07:45, 21 September 2006 (UTC)

Ok, that may be true. If so, then perhaps a sentence like "In sailing, and especially in sailboat racing, apparent wind is a vitally important factor, when determining the Points of sail a sailboat can successfully travel in" would be more appropriate than the current text. Do you agree? I believe this sentence is far less misleading than the one currently in the article. It's quite similar to the version before your edits, but I've made the end of the sentence a bit clearer, I think. Would this be a suitable middle ground, perhaps?

While I agree that a full discussion of sail trim and upwind tacking angles is beyond the scope of this article, I do think its important to mention why we sailors care about apparent wind to begin with. I guess the problem I have with the current version is that I don't think it adequately explains why. Thanks, Infinoid 23:35, 20 September 2006 (UTC)

• • • • • Points of sail

There is a an article Points of sail. It should not be necessary to duplicate information between apparent wind and points of sail. Duplication will make for incconsistency between articles as contributors to points of sail may not be well versed with the physics as those who may address apparent wind and error will occur and make updating difficult. Wikipedia must not become like a Tower of Babel

Tayana 21:28, 21 September 2006 (UTC)

Hi, Tayana. I agree there's already an article called Points of sail. That's why the sentence I proposed ("In sailing, and especially in sailboat racing, apparent wind is a vitally important factor, when determining the Points of sail a sailboat can successfully travel in") links to it. I do not believe this sentence duplicates any information, and I believe the sentence adequately covers the subject of sailing, so nothing more needs to be said about the subject. I hope you can clarify your perspective for me... are you suggesting that my proposed sentence is too complicated? Or are you saying we should remove all references to sailing from the Apparent wind article, altogether? At the moment, its unclear to me what you are trying to say. Thanks, Infinoid 20:55, 22 September 2006 (UTC)

• • • • Hello Infinoid,

Your sentence ("In sailing, and especially in sailboat racing, apparent wind is a vitally important factor, when determining the Points of sail a sailboat can successfully travel in") is OK and feel free to edit accordingly.

Tayana 21:17, 22 September 2006 (UTC)

• • • • Hi All.

IMO what is lacking is a clear definition of the marine term. The definition is valid, although focussed on the observer. Also, I would like to incude mathematical references to the vector calculation of apparent wind speed and angle.

My suggestion: Apparent Wind is the air flow relative to a moving object. Apparent Wind in marine terminology is the flow of air acting upon a sail, or the wind as it appears to the sailor. It differs from the true absolute wind observed by a stationary observer in velocity and direction.

Feuser 22:28, 4 June 2007 (UTC)

• Your suggestion is the same as that of classical definition of relative velocity as the moving object is the observer on the boat. The diagram shown, correctly identifies the apparent wind as the vector sum of the true wind Minus the boats vector. Thus the use of reciprocal of boats velocity is correct, and has been incorrectly removed. Please explain logic of your revision. Can you show some results for your formulae for Apparent wind magnitude and diretion for true wind angles of 45 90 135 and 180 degrees relative to the bow?

01:00, 11 June 2007 (UTC)

• • • The term reciprocal seems incorrect in that it suggests a fraction (1/x) not multiplication by -1 (negative value) of a number.

http://simple.wikipedia.org/wiki/Reciprocal

http://www.mathsteacher.com.au/year7/ch04_frac/06_recip/num.htm

• Example 1: Beam Reach (25 knots in 18 knots true)

a = 90

W = 18

H = 25

A = sqrt((25+18*cos(90))^2 + (18*sin(90))^2)

A = sqrt((25+0)^2 + (18*1)^2)

A = sqrt (625 + 324)

A = 30.80

• Example 2: Angle of apparent Wind in going 10 in 10 knots on a beam reach (deduction of angle using inverse cosine)

W = 10

H = 10

a = 90

b = angle of apparent wind

A = velocity of apparent wind = sqrt((H+W*cos(a))^2 + (W*sin(a))^2) AcosD = inverse cosine in degrees

b = AcosD((H+(W×COS(a)))/A)

b = AcosD ((10+(10/14.14213562373)

b = AcosD 1.41421356237

b = 45

• Example 3:

Angle and velocity of apparent wind in going 35 in 30 knots on a broad reach (115 deg)

W = 30

H = 35

a = 115

b = angle of apparent wind in degrees

A = velocity of apparent wind

b = AcosD((H+(W*cos(a))/sqrt((H+W*cos(a))^2 + (W*sin(a))^2))

A = sqrt ((30+35*-0.42261826174)^2+(30*0.90630778704)^2)

b = 47.14

A = 35.17

I believe using the variable H (head wind) summarizes more clearly the actual effect of boat speed (velocity) over ground. My apologies if my re-write deleted parts of your article - I feel your contributions were valuable and I believe the reference to classical mechanics was correct. However the term relative in the core definition would be misleading as it is used in the contrext of general relativity in the linked article.

Feuser 03:28, 13 June 2007 (UTC)

Hey 194.46.241.162

I think the latest addition is not only confusing but also a regression:

"This is the Inverse (mathematics) of the objects actual velocity or more succinctly the apparent wind is defined as the Velocity of the wind minus the Velocity of the object."

We've already established that "Apparent wind is the vector sum of the True Wind Velocity and the air stream generated by an "object's Velocity over ground".

The air stream generated by the objects' "Velocity over ground" is, in fact, the sum of the inverse velocity of the object and any current or displacement of the base medium. Therefore the effect of the objects motion relative to the wind is summarized as "head wind" (H).

Edit by Joern [83.21.158.93]: I have to state as a sailor, that the formulas are wrong. the Objects velocity must not be subtracted from the cosine term but rather beeing added to it. —Preceding unsigned comment added by 83.21.158.93 (talk) 08:08, 28 April 2009 (UTC)

Edit Feuser: Take a boat going dead downwind at 8 knots in 10 knots true. Your apparent wind will be 2 knots. I also removed redundant language from the Definition section. The movement of the vessel does not need to be described in order to convey the fact that the apparent wind is different from the true wind acting upon a stationary object. The following paragraph serves to explain the physics.

Wikipedia Terminology Conflict: "Headwind"

In this article, headwind is defined as the component of apparent wind that's due to an object's velocity, and is a vector that adds to true wind. Compare this to the Wikipedia article on Tailwind (there's no Headwind article), which states "A tailwind is a wind that blows in the direction of travel of an object, while a headwind blows against the direction of travel." In other words, a headwind doesn't add to true wind, it is true wind.

This is a direct contradiction that needs to be resolved. I suspect that the aeronautics-oriented tailwind article is correct while this article needs to adopt a better term.